Sulfur emission factor

A U. S. national biogenic sulfur emissions inventory with county spatial and monthly temporal scales has been developed using temperature dependent emission algorithms and available biomass, land use and climatic data. Emissions of dimethyl sulfide (DMS), carbonyl sulfide (COS), hydrogen sulfide (H2S), carbon disulfide (CS2), and dimethyl disulfide (DMDS) were estimated for natural sources which include water and soil surfaces, deciduous and coniferous leaf biomass, and agricultural crops. The best estimate of 16100 MT of sulfur per year was predicted with emission algorithms developed from emission rate data reported by Lamb et al. (1) and is a factor of 22 lower than an upper bound estimate based on data reported by Adams et al. 

Monthly emissions of COS, CS2, DMDS, DMS and H2S are calculated for each of the 3071 contiguous U. S. counties. In addition to the source factors described above, mean monthly temperatures compiled in the Geoecology Data Base provide the inputs required for the estimation of natural sulfur emissions. 

Direct evaluation of the accuracy of the emission rate estimates compiled in this natural sulfur emissions inventory is difficult. Our limited understanding of natural sulfur release mechanisms and the wide variety of possible environmental conditions to which the observed data must be extrapolated require a simplified approach to this complex process. A sensitivity analysis of the important components of the modeling procedure can be used indirectly to evaluate the uncertainty which should be associated with the model. The major components affecting the estimation of natural emissions in this inventory are source factors, temperature estimates, emission prediction algorithms and emission rate data. 

Three areas of uncertainty in this present inventory of natural sulfur emissions which need further work include natural variability in complicated wetland regions, differences in emission rates in the corrected SURE data and those reported by Lamb et al. (1) and Goldan et al. (21) for inland soil sites, and biomass emissions for which only a very limited data base easts. The current difficulty in determining the sources of variability emphasizes the need to better understand natural sulfur release mechanisms. At present, it may be useful to consider the emission rates based on the corrected SURE data as an upper bound to natural emissions and use the emission rates based on data described by Lamb et al. (1) as a more conservative estimate of natural sulfur emissions. However, this still leaves a factor of 22 difference between the suggested upper bound and our best current estimate. 

The temperature dependent algorithms used to predict natural sulfur emissions do not account for all of the variation in observed emissions. Other important environmental parameters may include, but are not limited to, tidal flushing, availability of sulfur, soil moisture, soil pH, mineral composition, ground cover, and solar radiation. A more accurate estimation of the national sulfur inventory will require a better understanding of the factors which influence natural emissions and the means to extrapolate any additional parameters which are determined to be important. 

Miller, J. M. Tellus. in press) have examined the transport of North American sulfur emissions across the north Atlantic Ocean to Europe. In a review of available precipitation-sulfate data from the north Atlantic and adjacent coastal regions, they report a concentration field consistent with known source distributions and meteorological factors. The excess sulfate concentration of marine background... 

Understanding the processes that control atmospheric aerosol concentrations and representing these processes in chemical transport models rests in large part on the accuracy of emissions inventories of aerosols and gaseous precursors. The most widely applied approach to developing such inventories is characterization of emissions per unit of activity (called emission factors ) combined with characterization of the intensity and geographic distribution of these activities. This approach is well developed for some gas-phase species. Emission of SO2 from fossil fuel combustion provides an example. Most sulfur in... 

Consequently, an intensive uptake of sulfur occurs in hydrosphere, lithosphere, and biosphere. This is the main reason that the content of gaseous sulfur species in the atmosphere is rather small and even in polluted air does not exceed 2-3 ppmv. In unpolluted atmosphere the concentration of most S compounds is at ppbv levels, despite the intense sulfuroutgassing from the Earth s interior. The atmospheric content of the major gaseous S species, either SO2 or H2S, is highly variable and is influenced by both natural and anthropogenic factors. The role of anthropogenic sulfur emission in acid rain chemistry will be discussed in Chapter 10. The influence of natural parameters, microbiological activity in particular, is described in Box 7. 

A breakdown of processes causing the release of S02 from anthropogenic sources is shown in Table 10-8. The combustion of coal now contributes 60% to all such emissions, that of petroleum and its products 28%, and the smelting of nonferrous ores as well as miscellaneous industrial processes take up the remainder. Individual emission estimates are derived as usual by combining statistical production data with emission factors. Fossil fuels contain sulfur primarily in the form of organic sulfur compounds. Combustion turns them into S02, which is vented with the flue gases. The ashes retain very little sulfur, so that emission factors for coals correspond closely... 

Nonferrous ores occur mainly in the form of pyrites. The large emission factors associated with nonferrous metal production derive from the fact that sulfur contained in the ores escapes mostly as S02 in spite of control measures. The most significant contribution to S02 emissions from industrial processes lies in the manufacture of sulfuric acid. The conversion of pulp to paper leads to emissions of H2S and organic sulfides, but their magnitude is comparatively small. The combustion of natural gas, which is another important source of energy, causes negligible sulfur emissions so that it is not even listed in Table 10-8. This fuel has a low sulfur content to begin with, and almost all of it is removed before use. 

Emission factors represent the amount of any gas emitted into the atmosphere upon burning or any other technological operations that proceed the oxidation of organic and inorganic sulfur to sulfur dioxide, per unit of product. 

Emission factors for sulfuric acid production are 27.4 kg/ton acid for traditional technology and only 3.3-5.3 kg/ton acid for the advanced technologies. During smelting of sulfide ores, a simple stoichiometric relationship is assumed to give SO2 released per metal production in kg/ton 2000 for copper (CuFeS2) KXX) for zinc (ZnS) and 320 per lead (PbS). The effectiveness of desulfurization in this industry was about 50% in China during 1990-1995. 

An estimate of emissions of a species from a source is based on a technique that uses emission factors, which are based on source-specific emission measurements as a function of activity level (e.g., amount of annual production at an industrial facility) with regard to each source. For example, suppose one wants to sample a power plant s emissions of S02 or NO. at the stack. The plant s boiler design and its fuel consumption rate are known. The sulfur and nitrogen content of fuel burned can be used to calculate an emissions factor of kilograms (kg) of S02 or NO emitted per metric ton (Mg) of fuel consumed. 

EF)i is the emission factor (amount of emissions per unit activity, for example, kg sulfur emitted per kg coal burned), and Pu, P2i... are parameters that apply to the specified source types and species in the inventories (for example, sulfur content of the fuel, efficiency of the eontrol technology). Top-down methodologies, also known as inverse modeling, derive emission estimates by inverting measurements in combination with additional information, such as the results of atmospheric transport and transformation models. 

Other emissions include gaseous emissions such as carbon monoxide, hydrocarbons, sulfur oxides, nitrogen oxides, hydrogen oxides, VOCs, and aldehydes. Gaseous anissions are much lower than the particulate, generally mounting to less than 0.5 kg/t. The EPA emission factors for various gaseous pollutants in asphalt concrete manufacture are listed in Table 53.16. 

The annual amount of sulfur deposited is relatively uniform from state to state (every state is within a factor of 2 of the average), in contrast to the wide variation in sulfur emissions among states. This tmiformity is due to the large-scale transport and mixing of sulfur in the atmosphere. 

Over the years, larger quantities of sulfur have been recovered for a number of reasons. These iaclude iacreased petroleum refining and natural-gas processiag, more stringent limitations on sulfur dioxide emissions, and higher sulfur contents of the cmde oil refined. Another contributiag factor is the lower sulfur content limits set on petroleum-based fuels. 

More recentiy, sulfuric acid mists have been satisfactorily controlled by passing gas streams through equipment containing beds or mats of small-diameter glass or Teflon fibers. Such units are called mist eliminators (see Airpollution control methods). Use of this type of equipment has been a significant factor in making the double absorption process economical and in reducing stack emissions of acid mist to tolerably low levels. 

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